Method for processing high-pressure vapor-discharge arc tube



1955 J. D. SMITH ETAL 3, 79,877

METHOD FOR PROCESSING HIGH-PRESSURE VAPOR-DISCHARGE ARC TUBE Filed 090-51, 1963 EXHAUST ARGON SUPPLY WITNESSES h INVSENTRPS d do n D. mi onDaniel A. Larson.

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- ATTORNEY United States Patent vania Filed Dec. 31,1963, Ser. No.334,795 4 Claims. (Cl. 316-16} This invention relates to dischargedevices and, more particularly, to a method for processing an arc tubefor a high-pressure vapor-discharge lamp of the mercuryadditive type.

It is known to modify high-pressure mercury-vapor discharge lamps byincluding additive materials, and particularly selected metalliciodides, in the arc tube. In the operation of such devices, the mercury,which is fully vaporized, establishes the proper loading or voltage dropacross the lamp and the additive iodides improve the color and luminousoutput of the discharge. Such so-called additive lamps are generallydisclosed in Illuminating Engineering, June 1963, article titled HigherEfiiciency Light Source Through Use of Additives to Mercury Discharge.

The introduction of discharge-sustaining material into the arc tube ofthe discharge device is generally known in the art as dosing.Heretofore, when dosing the discharge-sustaining materials into the arctube for a socalled mercury-additive-type lamp, the mercury has beenplaced into the arc tube in predetermined amount and the additiveiodide, such as sodium iodide, thallium iodide, or thin iodide, forexample, is also introduced directly into the arc tube, along with apredetermined pressure of inert ionizable starting gas. Any impuritieswhich are contained in the arc tube, or are introduced into the arc tubewith the discharge-sustaining material, are objectionable since they mayreact with the components comprising the arc tube or create a tendencyfor hard starting of the arc tube. By hard starting is meant that thearc tube requires a greater-than-desired voltage to initiate the arc.Since such discharge devices are intended to operate in standardfixtures wherein the starting voltage is fixed, any undue increase inthe required starting voltage for the lamp can result in an apparentfailure. In the case of metallic halide additive material, difiicultiesare encountered in purifying and maintaining the purity of the additivematerial before it is introduced into the arc tube.

It is the general object of this invention to provide a method ofclosing a partially fabricated, high-pressure vapor-discharge arc tubeof the mercury-additive type with a discharge-sustaining filling, inorder that substantially no deleterious impurities will be introducedinto the arc tube during the dosing process.

It is another object to provide a method for dosing a partiallyfabricated mercury-additive type of arc tube in order that the sealedarc tube will have a predetermined low starting voltage.

The aforesaid objects of the invention, and other objects which willbecome apparent as the description proceeds, are achieved by introducinginto a partially fabricated arc tube, prior to scaling such tube, apredetermined pressure of inert ionizable starting gas, a predeterminedamount of mercury which is at least in part chemically combined with apredetermined amount of selected halogen, and a predetermined amount ofadditive metal which will react with mercury halide to form additivemetal halide. The proportions of the dischargesustaining filling arecarefully controlled so that the amount of mercury introduced into thearc tube will establish a predetermined mercury-vapor pressure in thearc tube during operation. The total halogen which is introduced intothe arc tube in the form of mercury halide is so controlled that it willreact with the additive metal which is placed into the arc tube and forma predetermined amount of additive metal halide, in order to provide thearc tube, when operated, with the desired spectral output andefiiciency. The total amount of additive metal which is introduced intothe arc tube is selected so that it is at least sufficient to react withall of the halogen constituent of the mercury halide which is introducedinto the arc tube.

For a better understanding of the invention, reference should be had tothe sole figure of the drawing which illustrates a partially fabricatedarc tube wherein a predetermined amount of mercury iodide, mercury, andadditive metal have been introduced into the arc tube along with apredetermined pressure of argon starting gas, and the arc tube is aboutto be sealed by tipping off the exhaust and dosing tubulation.

While the teachings of the present invention are applicable to lamps ordischarge devices of varying size and designed wattage input,high-pressure vapor-discharge lamps having a designed power input of 400watts are used extensively, and hence an arc tube for such a lamp hasbeen illustrated and will be so described.

With specific reference to the arc tube processing operation asillustrated in the drawing, the arc tube 10 in its partially fabricatedform comprises an elongated envelope 12 which is formed oflight-transmitting refractory material such as quartz or polycrystallinealumina. Main operating electrodes 14 are disposed proximate either endof the envelope 12 and are connected to leadin conductors 16 sealedthrough the ends of the envelope 12, which lead-in conductors includeribbon-type seals 18. As is usual, a starting electrode 20 is positionedproximate one of the main electrodes 14. Extending from a side of theenvelope 12 is an elongated exhaust and filling or dosing tubulation 22.Prior to sealing the arc tube 10, a predetermined amount of mercuryiodide powder 24, a predetermined amount of tin powder 26, and apredetermined amount of mercury 28 are placed into an upright capsulehaving an open end and positioned in the elongated tubulation 22. Thetubulation is connected to a conventional exhaust and gas-filling head30 and the arc tube is baked, exhausted and gas-filled with apredetermined pressure of inert ionizable starting gas, such as 20 mm.of argon. The are tube and tubulation are then inverted to dose themercury, mercury iodide and tin from the capsule and into the arc tube.This general technique of closing is conventional and the capsule is notshown. After the discharge-sustaining filling has been introduced intothe envelope 12, the envelope is tipped ofi by means of a conventionalgas-air burner 32, as shown in the drawing, in order to complete the arctube fabrication.

As a specific example, the arc tube 10 is designed to be operated with apredetermined power input of 400 watts, the distance between theoperating electrodes 14 is approximately 67 mm. and the arc tubeencloses a predetermined volume of approximately 22 cc. A specificdischarge-sustaining filling desired for the operating arc tube ismercury in amount of 66 mg, stannous iodide in amount of 15 mg, andargon starting gas in such amount that the argon pressure in the coldarc tube is 20 mm. Hg. This amount of mercury is completely vaporizedduring lamp operation and with the tin iodide provides the lamp with anoperating potential of approximately volts. In the case of mostso-called mercury-additive lamps, the vaporized mercury accounts fornearly all of the voltage drop across the lamp. Tin iodide additive, incontrast, has a relatively low boiling temperature, thus accounting forabout 30% of the measured voltage drop for the specific lamp consideredhereinbefore.

In dosing the foregoing specific lamp in accordance with the presentinvention, 18 mg. of mercuric iodide powder and 58 mg. of mercury areadded to the arc tube along with 4.7 mg. of tin powder. In addition,argon starting gas at a pressure of 20 mm. Hg is included in the arctube, after which the arc tube is sealed by tipping off. If desired, asmall amount of tin powder may be added over that which is required toreact stoichiometrically with the mercury iodide to form stannousiodide. Alternatively, the mercury as added to the arc tube could all bein the form of the iodide, which of course would require that the addedtin be increased by such amount as required at least to reactstoichiometrically with the added mercury iodide to form stannousiodide.

It should be clearly understood that the total amount of mercury whichis introduced as free mercury and as the iodide into the arc tube ispredetermined in accordance with that operating voltage which is desiredto be developed across the lamp lead-in conductors 14.

The determination of the proper amount of mercury to achieve apredetermined voltage drop for any specific lamp is well known, and isgenerally described in US. Patent No. 2,892,665, dated June 30, 1959. Ifthe present lamp were desired to be operated under either higher orlower voltage and power conditions, or the arc tube volume was modified,the proper charge of mercury to provide such a desired operating voltagecould be readily determined. When the arc tube is first operated, theadded tin powder reacts with the mercury iodide to form metallic mercuryand tin iodide. The total halogen, such as the iodine, which isintroduced to the arc tube in the form of mercury halide, when reactedwith the finely divided additive metal, establishes a predeterminedpressure of additive metal halide during normal operation of the arctube, in order to provide desired discharge characteristics. Thetotalamouut of the finely divided or powdered additive metal, such astin, which is introduced into the arc tube is at least sufficient toreact with all of the halogen constituent of the mercury halide which isintroduced into the arc tube. The inert, ionizable starting gas fill inthe arc tube can be modified considerably with respect to the gas usedand the gas pressure.

As noted hereinbefore, the powdered metallic additive metal can bepresent in amounts which are substantially greater than those requiredto react stoichiometrically with the halogen which is introduced withthe mercury. Such additional amounts of additive metals may be desirablein some cases.

While an iodide additive is preferred, bromides or chlorides can also'be substituted in whole or in part for the iodide, with mercury bromideor mercury chloride added to the arc tube in powder form in accordancewith the present invention. Similarly, while a tin additive is useful toprovide a very white light when combined with the iodide, other additivemetals such as powdered zinc, thallitun, sodium, thorium, gallium,indium, cadmium, calcium or barium, or mixtures thereof, can besubstituted in while or in part for the tin and placed in powder forminto the arc tube when it is being processed in accordance with thepresent invention. The state of division of the powdered additive metalis not critical and the addi tive metal can be added as a slug, ifdesire. The amount of added metallic halide desired in the operating arctube will vary. As an example, such halide can be present in totalgram-mole amount which is equivalent to the tin iodide additive exampleas previously considered.

Since mercury iodide or the other specified mercury halides can bepurified to a very high degree, and the additive metals can also beobtained in very pure form, are tubes processed in accordance with thepresent invention normally display improved performance as compared tootherwise similar arc tubes which have been processed by dosing theadditive materials directly into the arc tube as metallic halide. Thisis because the metallic halides per se are difiicult to obtain andmaintain in very pure form. As a result, when such metallic halide isdosed directly into the arc tube, it carries with it some deleteriousimpurity constituents which are later released. These releasedimpurities can manifest themselves by reacting with the arc tubecomponents or by remaining as a gas in the arc tube, thereby creatinghard starters.

It will be recognized that the objects of the invention have beenachieved by providing an improved method for dosing a mercury-additivetype are tube for a gaseous discharge device in order that the processedarc tube will have improved operating characteristics.

While a :best embodiment has been illustrated and described in detail,it is to be particularly understood that the invention is not limitedthereto or thereby.

We claim as our invention:

1. The method of dosing a partially fabricated highpressurevapor-discharge arc tube of the mercury-additive type with adischarge-sustaining filling, which are tube when completely fabricatedenclosed a predetermined volume and is adapted to be normally operatedwith a predetermined power input, which method comprises: introducinginto said partially fabricated arc tube a predetermined pressure ofinert ionizable starting gas, a predetermined amount of mercury at leastpart of which is chemically combined with a predetermined amount ofselected halogen, and a predetermined amount of selected additive metalwhich will react with mercury halide to form additive metal halide; thepredetermined amount of mercury introduced into said are tube, whencompletely vaporize during normal operation of said are tube,establishing a predetermined vapor pressure in said are tube; the totalhalogen introduced into said are tube in the form of mercury halide,when reacted with said finely divided additive metal; forming apredetermined amount of additive metal halide in said are tube; and thetotal amount of said additive metal introduced into said are tube beingat least suliicient to react with all of the halogen constituent of themercury halide introduced in said are tube to form additive metalhalide; and sealing said arc tube after introducing saiddischarge-sustaining filling into said are tube.

2. The method as specified in claim 1, wherein said mercury halide is atleast one material of the group consisting of mercury iodide, mercurybromide, and mercury chloride.

3. The method as specified in claim 1, wherein said additive metal is atleast one finely divided metal of the group consisting of tin, zinc,thallium, sodium, thorium, gallium, indium, cadmium, calcium, andbarium.

4. The method of dosing a partially fabricated highpressurevapor-discharge arc tube of the mercury-tin iodide type with adischarge-sustaining filling, which are tube when completely fabricatedencloses a predetermined volume and is adapted to be normally operatedwith a predetermined power input, which method comprises: introducinginto said partially fabricated arc tube a predetermined pressure ofinert ionizable starting gas, a predetermined amount of mercury at leastpart of which is chemically combined with a predetermined amount ofiodine, and a predetermined amount of tin; the predetermined amount ofmercury introduced into said are tu'be, when completely vaporized duringnormal operation of said are tube, establishing a predetermined vaporpressure in said arc tube; the total iodine introduced into said aretube in the form of mercury iodide, when reacted with said finelydivided tin, forming a predetermined amount of tin iodide in said aretube; and the total amount of said tin introduced into said are tubebeing at least suflicient to react with all of the iodine constituent ofthe mercury iodide dosed into said are tube to form tin iodide; andafter introducing said discharge-sustaining filling into said arc tube,seaing said are tube.

No references cited.

FRANK E. BAILEY, Primary Examiner.

1. THE METHOD OF DOSING A PARTIALLY FABRICATED HIGH PRESSUREVAPOR-DISCHARGE ARC TUBE OF THE MERCURY-ADDITIVE TYPE WITH ADISCHARGE-SUSTAINING FILLING, WHICH ARC TUBE WHEN COMPLETELY FABRICATEDENCLOSED A PREDETERMINED VOLUME AND IS ADAPTED TO BE NORMALLY OPERATEDWITH A PREDETERMINED POWER INPUT, WHICH METHOD COMPRISES: INTRODUCINGINTO SAID PARTIALLY FABRICATED ARC TUBE A PREDETERMINED PRESSURE OFINERT IONIZABLE STARTING GAS, A PREDETERIMNED AMOUNT OF MERCURY AT LEASTPART OF WHICH IS CHEMICALLY COMBINED WITH A PREDETERMINED AMOUNT OFSELECTED HALOGEN, AND A PREDETERMINED AMOUNT OF SELECTED ADDITIVE METALWHICH WILL REACT WITH MERCURY HALIDE TO FORM ADDITIVE METAL HALIDE; THEPREDETERMINED AMOUNTED OF MERCURY INTRODUCED INTO SAID ARC TUBE, WHENCOMPLETELY VAPORIZE DURING NORMAL OPERATION OF SAID ARC TUBE,ESTABLISHING A PREDETERMINED VAPOR PRESSURE IN SAID ARC TUBE, THE TOTALHALOGEN INTRODUCED INTO SAID ARC TUBE IN THE FORM OF MERCURY HALIDE,WHEN REACTED WITH SAID FINELY DIVIDED ADDITIVE METAL; FORMING APREDETERMINED AMOUNT OF ADDITIVE METAL HALIDE IN SAID ARC TUBE; AND THETOTAL AMOUNT OF SAID ADDITIVE METAL INTRODUCED INTO SAID ARC TUBE BEINGAT LEAST SUFFICIENT TO REACT WITH ALL OF THE HALOGEN CONSTITUENT OF THEMERCURY HALIDE INTRODUCED IN SAID ARC TUBE TO FORM ADDITIVE METALHALIDE; AND SEALING SAID ARC TUBE AFTER INTRODUCING SAIDDISCHARGE-SUSTAINING FILLING INTO SAID ARC TUBE.